[A comparison of archwires of memory alloys Nitinol, NiTi Ormco and Tru-chrome which were subjected to edgewise torsion of 20 degrees, 25 degrees, 30 degrees and 35 degrees and a temperature of 37 degrees Celsius].

Nickel-titanium (Nitinol, NiTi Ormco) and stainless steel (Tru-chrome) orthodontic archwires were studied by means of torsion test at 37 degrees Celsius. At small activations (20 degrees, 25 degrees, 30 degrees) nickel-titanium wires have a comparable stiffness to stainless steel wires. At larges activations (from 35 degrees) nickel-titanium wires produce lower moments than stainless steel wires. At 35 degrees of activation the average stiffness of NiTi Ormco is 56% that of Tru-chrome. At 35 degrees of activation the average stiffness of Nitinol is 43% that of Tru-chrome.